The present invention relates to a device, called a scrap melter, for submerging scrap metal in a molten metal bath. The device preferably includes a drive source, an impeller and a drive shaft. The device preferably draws molten metal downward in order to submerge scrap placed on the surface of the bath.
Scrap melter systems, such as the one shown schematically in FIGS. 1 and 2, generally use two devices, a circulation pump and a scrap melter. As shown in FIG. 1 the vessel V containing molten metal bath B is preferably divided into two compartments. Compartment 1 (called a pump well) houses circulation pump 2. Compartment 3 (called a charge well) houses a scrap melter 10. The circulating molten metal moves between compartment 1 and compartment 3 and is preferably circulated throughout vessel V. Scrap S is introduced into compartment 3 and is submerged by the downward draw created by the impeller of scrap melter 10, which pulls the scrap downward into the molten metal bath. The molten metal bath is preferably maintained, at least partially, in a remelting furnace having a heating chamber interconnected to a melting chamber. Bath B is maintained at a temperature above the melting point of the scrap metal in order to melt the scrap metal.
A conventional scrap melter includes an impeller affixed to a drive shaft, and a drive source for rotating the shaft and the impeller. As stated above, the impeller draws molten metal and the scrap metal downward into the molten metal bath in order to melt the scrap. The circulation pump is preferably positioned in the pump well and circulates the molten metal between the chambers in order to maintain a relatively constant temperature within bath B. Such a system, including a circulation pump and a scrap melter, is disclosed in U.S. Pat. No. 4,598,899, issued Jul. 8, 1986 to Cooper, the disclosure of which that is not inconsistent with this disclosure is incorporated herein by reference. As defined herein, the terms auger, rotor and impeller refer to the same general structure, i.e., a device used in a scrap melter for displacing molten metal.
Scrap melter impellers generally move molten metal radially outward away from the impeller to create a downward draw above the impeller. However, such impellers can create turbulence or flow that may partially move into the path of the fluid entering the impeller from above, in which case some scrap may not be efficiently drawn into bath B where it can be melted and mixed, thus decreasing the fluid flow to the impeller and decreasing the efficiency of the scrap melting operation. In addition, the radial turbulence may cause some fluid that has been expelled from the impeller to be immediately recirculated through the impeller, thus decreasing the flow of virgin fluid through the impeller. That further decreases efficiency because it reduces the draw of molten metal from above the impeller. As a result, in order to maintain a desired volume of fluid flow through the impeller, the speed of the impeller may be increased to overcome these effects. Increasing the speed of the impeller, however, may cause excess vibration leading to part failure, downtime and maintenance expenses.
Scrap melters have been developed to restrict radial flow from the impeller to limit turbulence and produce more efficient flow. One such assembly, disclosed in U.S. Pat. No. 4,930,986, issued Jun. 5, 1990 to Cooper, the disclosure of which that is not inconsistent with this disclosure is incorporated herein by reference, includes an impeller positioned inside a drum, both of which rotate as a single unit. One disadvantage to this assembly is that pieces of scrap or dross can jam in it, which decreases its efficiency. Other prior art devices are disclosed in U.S. Patent Nos. 4,286,985, 3,984,234, 4,128,415 and 4,322,245.
The preferred embodiment of the present invention is a scrap melter utilizing an open impeller to reduce jamming or clogging. Thus, the invention can function efficiently in virtually any scrap melting environment, handling particles of virtually any size that are likely to be encountered in any such environment. An impeller according to the invention functions by displacing molten metal to create a downward draw. It provides the benefit of reducing the problems associated with faster operating speeds (i.e., the possible creation of a vortex and turbulence, and/or part failure, greater downtime and higher maintenance costs). The way in which it achieves these results is by (a) displacing more molten metal while operating at the same speed as conventional impellers, and/or (b) moving at least some of the molten metal in a downward or partially downward direction.
An impeller according to the invention displaces more molten metal by the use of (1) a larger area on the blade surfaces that push against the molten metal as the impeller rotates, and/or (2) surfaces that push against the metal at angles that displace a relatively large amount of molten metal. One impeller according to the invention preferably moves molten metal at least partially in the downward direction, while another moves molten metal only in an outward direction.
In one preferred embodiment the impeller is preferably a four-bladed cross wherein each blade preferably includes an angled surface that directs molten metal at least partially in the downward direction. The impeller creates a draw that draws molten metal and any solid scrap metal contained therein downward into the molten metal bath. It also preferably provides at least some radial or partially radial flow, and may include a surface or structure specifically designed to generate radial or partially radial flow, to assist in circulating molten metal within the bath.
In another preferred embodiment, the impeller is preferably a four-bladed cross wherein each blade preferably includes a vertical surface that directs molten metal radially outward away from the impeller. The impeller creates a draw that draws molten metal and any solid scrap metal contained therein downward into the molten metal bath. It also assists in circulating molten metal within the bath.
A scrap melter according to the invention can be operated at lower speeds than conventional melters but still displace the same amount of molten metal per impeller revolution. Alternatively, it can be operated at the same speeds as, and displace more molten than conventional scrap melters. A benefit of the lower speed is that the scrap melter of the invention vibrates less and requires less maintenance and fewer replacement parts.
A preferred melter according to the invention includes a drive source, a drive shaft having a first end and a second end and an impeller. The first end of the drive shaft is connected to the drive source. An impeller according to the invention is connected to the second end of the drive shaft. The drive source is preferably a pneumatic or electric motor, but can be any device(s) capable of rotating the impeller.
A scrap melter according to the invention may be used in a scrap melter system comprising a scrap melter, a vessel containing a molten metal bath and a circulation pump. Conventional pumps for pumping molten metal that may be used as circulation pumps are generally disclosed in U.S. Pat. No. 2,948,524 to Sweeney et al., U.S. Pat. No. 5,203,681 to Cooper entitled xe2x80x9cSubmersible Molten Metal Pump,xe2x80x9d pending U.S. application Ser. No. 08/59,780, filed Dec. 13, 1996, entitled Molten Metal Pump With a Flexible Coupling and Cement-Free Metal-Transfer Conduit Connection, U.S. Pat. No. to Cooper entitled Impeller Bearing System for Molten Metal Pumps, U.S. application Ser. No. 09/152,168, filed Sep. 11, 1998, entitled Improved Gas Dispersion Device, U.S. Pat. No. 5,678,807 to Cooper and U.S Pat. No. 5,662,725 to Cooper, the disclosures of which are incorporated herein by reference.